56 GENEEAL HISTOHY OF THE INFTJSOEIA. 



" The rapidity with which each individual frustiile moves is in direct rati 

 to its distance from the terminal stationary frustnle, being most rapid at the 

 opposite or moving extremity of the filament. On this account, most of the 

 friistules, while the filament is moving to and fro, cross a line drawn at right 

 angles to the middle of the long axis of the stationary frustule, at the same 

 instant of time, afterwards shooting past each other like horses on a race- 

 course. 



" The force with which the filament moves is very great, so much so that 

 I have observed it upset and shove aside a large fnistule of A. arenaria, n. 

 sp., at least six times its own bulk, obstructing its path. This force is, in a 

 great measiu-e, due to the rapidity with which the frustules move, — the time 

 which a filament, even of considerable length, occupies in crossing the field 

 of the microscope being only a few seconds. 



" Light appears to be a necessary stimulus for the maintenance of this 

 motion. When a filament in active motion is placed in the dark for a short 

 period, and then examined, the movement is seen to have ceased, but again 

 commences when the filament is exposed to the light for a short time. Is 

 not this singular movement, Tvith which the present species is endowed, a 

 vital phenomenon, and independent of physical causes for its existence ? 



'^ When the moving extremity becomes entangled in any kind of substance 

 intercepting its coui'se, the opposite or stationary extremity commences to 

 move, and continues to do so until the entangled extremity is set free ; 

 sometimes, in such instances, a frustule in the centre remains fixed, a move- 

 ment of each half of the filament in opposite directions, on either side of it, 

 taking place. But all these irregularities cease as soon as the impediment 

 has been got rid of. 



" These facts lead to the conclusion that the present species is a true Bacil- 

 laria, although aiDparently somewhat anomalous in the structure of its frustule. 

 The gliding movement of one fi'ustule over the contiguous one is the same as 

 is observed in B. paradoxa ; but it difi'ers from this latter species in this 

 essential particular, that the wlioU of its filament moves on one side of a 

 terminal frustule which is stationary, — while, in B. paradoxa, each half of the 

 filament moves in opposite directions on either side of a central stationary 

 frustule." 



The movement of one segTaent upon another is witnessed in other con- 

 catenate species, but in a less degree, where the medium of attachment is 

 limited to a small space, as in those several genera having the alternate or 

 opposite angles of their frustules connected by a link-like isthmus, e. g. 

 Diatoma, Fragilaria, Grammatophora, &c. 



Nutritive Fitnctions; — Supposed Stomachs; — Circulation of Contents; — 

 Kespiration. — The nutrition of Diatomeas is provided for primarily by the 

 endosmotic and exosmotic action going on through the ' foramina ' in the 

 silicious epiderm, whereby fluid material laden with the matters necassary 

 to build up the various elements of the endochrome is introduced into the 

 organisms. 



On the first appearance of a frustule, the endochrome is homogeneous and 

 granular ; but as time advances, granules are seen to congregate in certain 

 parts, and globules or vesicles of various size speedily develope themselves, 

 and either take up definite positions or are irregularly diffused. During 

 these changes in the contents — during, indeed, the entire life of _ the cell, 

 under the influence of light, oxygen is given off, and the gases -with which 

 it was united in various chemical compounds are appropriated to the purposes 

 of the economy. 



The veiT fact of the existence of the silicious epiderm, thrown off, it would 



